Laminar flow of fluids within microchannels has been studied for use in microfluidic fuel cells, which consist of an anode and cathode configured as a galvanic cell within a microchannel Parallel streams of fuel and oxidant flow across the anode and cathode, respectively, where electrochemical reactions occur when the potential difference between fuel and oxidant is thermodynamically favorable.
In many conventional reactive microfluidic channels (e.g., fuel cells), the rate of reaction declines along the length of the microfluidic channel. In fuel cells, this may lead to declines in current and power density. These effects may be explained in terms of the diffusion layer. The diffusion layer is the thin layer of liquid near the electrode surface where rapid changes in the concentration of oxidized or reduced species occurs during an electrochemical reaction. Under conditions of convective flow and high Peclet number, the diffusion layer is confined near the surface of the electrode analogous to Prandtl's boundary layer. As the electrochemical reaction proceeds, electroactive species are depleted cumulatively. As such, the leading edge of the electrode experiences a higher concentration of electroactive species relative to the trailing edge because the thickness of the diffusion layer is increasing along the length of the electrode. As the thickness of the diffusion layer increases, the average mass flux toward the electrode decreases along with the corresponding current and power density.
Accordingly, improved compositions and methods are needed.